The Collaborative International Dictionary of English v.0.48:

Withy \With"y\, n.; pl. Withies. [OE. withe, wipi, AS.
   w[imac]?ig a willow, willow twig; akin to G. weide willow,
   OHG. w[imac]da, Icel. v[imac]?ja, a withy, Sw. vide a willow
   twig, Dan. vidie a willow, osier, Gr. ?, and probably to L.
   vitis a vine, viere to plait, Russ. vite. [root]141. Cf.
   Wine, Withe.]
   [1913 Webster]
   1. (Bot.) The osier willow (Salix viminalis). See Osier,
      n.
      (a) .
          [1913 Webster]

   2. A withe. See Withe, 1.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Withy \With"y\, a.
   Made of withes; like a withe; flexible and tough; also,
   abounding in withes.
   [1913 Webster]

         The stream is brimful now, and lies high in this little
         withy plantation.                        --G. Eliot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

withy
    n 1: strong flexible twig [syn: withe, withy]